Method of incorporating color couplers in hydrophlic colloids



United States Patent METHOD OF INCOREORATKNG COLOR COU- PLERS IN HYDROFHEIC COLLOEDS Aaron Ben-Ezra, Eingharnton, N.Y., and Chester E. Rose, Montrose, Pa., assignors to General Aniline 8: Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed $ept. 30, 1959, Ser. No. 843,374

7 Claims. (Cl. 961llt9) This invention relates to a method of incorporating photographic chemical compounds, particularly color couplers in hydrophilic colloids, and especially in light sensitive silver halide gelatin photographic emulsions.

One of the earliest processes for using color formers in photographic emulsions was suggested in U.S.P. 1,055,155 issued to Rudolf Fischer in 1912. Fischer proposed a system of three layer color photography in which the couplers or color forming compounds were located in three different emulsion layers; wherein each coupler was capable of yielding upon reaction with the oxidation products of a primary amino development agent, a dye image, in a color complimentary to the sensitivity of the layer in which it was incorporated. Although the Fischer process was theoretically feasible, it did not prove successful in practice. The couplers which were then available were not fast to diffusion and tended to migrate from the emulsion layer in which they were incorporated into an adjoining emulsion layer, thus causing a color degradation of the final dye images.

Over the ensuing years, numerous improvements were suggested which dealt with modified color formers and techniques for their incorporation in photographic colloids. By synthesizing couplers containing a bulky group,

i.e., a long chain alkyl radical (see U.S.P. 2,186,849) attached to the molecule, their tendency to diffuse out of their respective sensitive emulsion layers was greatly reduced. The presence of this group imparts to the molecule a hydrophobic character. These long chain nondifiusing couplers also contain a salt-forming group, i.e., a carboxy or sulfo group which in the form of their alkali salts provides the couplers with water-soluble groups of hydrophilic character to permit their incorporation in aqueous gelatin silver halide emulsions. The simultaneous presence of hydrophilic and hydrophobic groups give these color formers a soap-like character.

While the above process produces excellent dye images free from color degradation, the incorporation into the emulsion of long chain high molecular weight couplers containing salt-forming groups poses a number of difliculties. In most instances, the corol formers are dissolved in a water, or water-alcohol solution, of an alkali metal hydroxide such as aqueous sodium hydroxide or alcoholic potassium sydroxide, and then added to the emulsions as a so-called coating final, as one of the last additives just prior to coating.

In most cases there is an extended, but varying, holding time between the addition of the color former solution to the silver halide emulsion and the actual application of the emulsions to the web or the film base. In many instanecs, there is a time interval between the completion of the rernelting and the end of the coating operation which may range between two and six hours.

It is very important that during this holding time the viscosity be held constant, because with the currently used coating techniques, dip-coat, metering or air knife, any variation or drift in viscosity will result in difierent coating thickneses. Thus, with a constant coating speed, an emuslion of lower viscosity will produce a thinner layer while a higher viscosity will result in a layer thicker than desired. Any change in thickness from standard will result'in an unbalanced color picture; the thinner 'ice layer will give a lower maximum density, while a heavier layer will produce an undesirable higher maximum density in the layer being coated.

This increase in viscosity on holding and during coat ing, is especially noticeable with emulsion formulations of relatively low water content and relatively high initial viscosity which contain color formers resistant to dif fusion, which are substituted by a water-solubilizing group and which are employed in the form of a water-soluble alkali metal salt. Surprisingly, the degree of viscosity increase on holding, depends to a large extent on the type of color former used. It is most pronounced with those color formers which contain a benzimidazol nucleus, which is further substituted by a long chain alkyl group attached to one of the nitrogen atoms and a sulfonic or carboxylic acid group.

It is, therefore, an object of this invention to provide a method for the incorporation of color formers in photographic emulsions.

A further object of this invention is to provide a method of incorporating in a hydrophilic, photographic colloid, color formers which are stable to diifusion and have an acid group as a substituent.

A further object of the invention involves the uniform 7 distribution of a color former in a liquid photographic gelatin silver halide emulsion while insuring that the viscosity of said silver halide emulsion does not increase materially on holding.

A still further object of this invention comprises a light sensitive gelatin silver halide emulsion containing a color former uniformly distributed through the gel matrix without the use of an alkali metal hydroxide solvent. Other objects will be apparent from the following description. These objects are accomplished by dissolving the chemical compounds, particularly the color formers fast to diffusion in dimethyl sulfoxide before adding them to the silver halide emulsion.

In preparinn g photographic emulsions ,the color formers are dissolved in dimethyl sulfoxide. The dimethyl sulfoxide solution of the color former is then diluted with water which may also contain other coating finals. The aqueous dimethyl sulfoxide solution is then added directly to a melted gelatin silver halide emulsion with 07 adequate stirring. In a second method, the solution of tin and the resulting mixture combined with a melted gelatin silver halide emulsion.

The amount of dimethyl sulfoxide employed varies somewhat with different color formers. In general amounts ranging from 5 to 35 parts by weight of dimethyl sulfoxide per 10 parts by weight of color'former have been found to be most satisfactory.

In preparing the color emulsion for coating, the usual coating aids, stabilizers and wetting agents such as saponin and/or synthetic surfactants which may be of the anionic, cationic, non-ionic or amphoteric type, are add ed prior to the addition of the color formers. Among such wetting agents are those described in United States Patents 1,970,578, 2,118,059, 2,240,476 and 2,768,894.

The color formers which have the strongest tendency to increase the viscosity on holding contain in their molecule, a jbenzimidazole nucleus which is substituted on the nitrogen atom in the 1-position by an alkyl chain of at least 10 carbon atoms and substituted in the 5-position by a water solubilizing group, in which the benzirnidazole nucleus is connected through its carbon atom in the 2- position to the residue of a color forming residue which is reactive with the oxidation products of a primary amino developing agent and contains a reactive methylene or ethenol or phenolic hydroxyl group. These color form- 3,050,394 3 I A; ers'are characterized by the following general formula: I Example 1 R2 Two hundred grams of 1-octadecyl-2-[2-(1-hydroxy- N/C-R wherein R is a radical containing a reactive methylene, ethenol or phenolic hydroxyl group capable of reacting with the oxidation products or an aromatic amino developing agent to form an azo-methine, indoaniline or phenazonium dyestuif, R is an alkyl chain containing at 'least carbon atoms, e.g., decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl and the like, and R is a water solu'bilizing group such as sulfo, carlboxy and the like.

More particularly, color formers which contain a benzimidazole nucleus as part of the molecule and which are capable of forming dye images upon development with a dialkylamino-aniline developing agent are illustrated by the following structural formulae:

and

wherein R is a hydroxy aromatic radical, such as substituted or unsubstituted hydroxynaphthyl, hydroxyphenyl Suitable examples of color formers embraced by these general formulae are disclosed in United States Patents 2,545,687 and 2,547,307, in which their method of preparation is also described;

Color formers substituted by a henzimidazole nucleus and capable of forming magenta 'phenazonium (azine) dye images upon development with triamindbenzene developers are described in United States Patent 2,486,440;

' color formers used with N,N-dialkylphenylenediamine developers are disclosed in United States Patent 2,701,766. They are characterized by the following general formula:

I OH

wherein R R and R have the same values as above;

R is'hydrogen, a carboxyalkyl, allyl or lower alkyl group; andR- is an allyl, lower alkyl, aryl or heterocyclic group.

The invention is further. illustrated by the following examples, but it is to be understood that .the invention is not restricted thereto. The parts and percentages are by weight unless otherwise stated. 7

naphthyl)]benzimidazole-5-sulfonic acid which is characterized by the following structural formula:

' was dissolved in 250 milliliters of dimethyl sulfoxide.

The resultant solution was diluted with 3750 milliliters of water and added to ten kilograms of a liquid gelatin silver halide emulsion sensitized to red light and containing about 8 percent of gelatin, 3 percent of silver bromoiodide, plus small amounts of saponin and sodium tetradecyl sulfate as wetting agents.

In a control sample, the color former was dissolved in 200 milliliters of 4 percent sodium hydroxide solution which was diluted with 3800 milliliters of water prior to addition of the emulsion.

Viscosity measurements were taken at various holding times (40 C.) with the followingresults:

Control (Sodium Hydroxide) Test (Dimethyl Sulfoxide) Time Relative Time Relative viscosity viscosity Q Hour 86.2 0 Hour 106. 6 V 2 Hours 113.8 2 Hours 112. 8 3 Hours 119.0 3 Hours 114. 2 4 Hours. 124. 2 4 Hours 113. S 5 Hours 129.0 5 Hours I v 113 .0

cosity of the emulsion'which contained thesodium hydroxide continued to increase with time. I

The emulsion with the dimethyl sulfoxide solvent wascoated onto a base and dried. It gave a coating of even thickness and even maximum density after development. The control emulsion, due to its continued increase in viscosity, showed variations in the developed color den sities between the start and the end of the coating.

Example II naphthyl] benzimidazoleJ-sulfonic acid having the follow ing structural formula: V a

was dissolved in 20 milliliters of dimethyl sulfoxide which i was prepared according to the method described in United States Patent 2,581,050. The resultant solution was added with stirring to 200,1nilliliters of water containing milligrams of the reaction product of 1 molar equiva lent of 2,6,8-dimethy'lnonanol-4 and l2.molar equivalents of ethylene oxide, and 1 gram of saponin. The resultant dispersion was added to l kilogram of a silver bromo-l. V

iodide emulsion having a gelatin concentration of 6 per cent and a silver 'salt concentration of 3 percent- The "emulsion was held for six hours. at 40 C. without an in crease in viscosity. 7 A control emulsion, in.which the color former had been incorporated by the use of sodium hydroxide, showed a continued viscosity increase during theholding time.

A u L-- Example 111 Example I was repeated except that a blue sensitive silver halide emulsion was used which contained 20 grams of the yellow color former, 2-(4'-benzoylacetaminophenyl)-1-octa-clecylbenzimidazole-S-sulfonic acid having the following structural formula:

which had been previously dissolved in 20 milliliters of dimethyl sulfoxide and then diluted with 380 milliliters of water. The relative viscosity of this silver halide emulsion remained constant during 5 hours holding at 40 C., whereas a control emulsion prepared by dissolving the coupler in aqueous sodium hydroxide, showed a relative viscosity increase of 50 percent.

Example IV Example 111 was repeated with the exception that the 20 grams of 2-(4'-benzoylacetaminophenyl)-1-octadecylbenzimidazole-S-sulfonic acid were replaced by 25 grams of 2 [(3',5-dibenzoylacetamino)phenyl]-l-octadecylbenzimidazole-S-sulfonic acid having the following struc- The viscosity of the emulsion containing the dimethyl sulfoxide did not increase during a 5 hour holding period at 40 C. However, the viscosity of the material prepared with sodium hydroxide, increased by about 60 percent during the same holding time.

Example V Sixty grams of the magenta color former 2-[4-(6-bromo S-hydroxy-Z-(2-sulfophenyl)-cinchoninoyl)-aminophenyl]-l-octadecyl-S-snlfonbenzimidazole, having the following structural formula:

SOEH were dissolved in 120 milliliters of dimethyl sulfoxide and diluted with 2 liters of water. The resulting solution was then added to kilograms of a green sensitive silver halide emulsion which contained about 6 percent of gelatin and 2 percent of silver bromoiodide. The viscosity of the resultant emulsions remained substantially unchanged during a six hour holding time, whereas a type emulsion in which the color former had been dissolved by the use of aqueous sodium hydroxide solution, showed a relative viscosity increase of over 50 percent.

While the present invention has been described with reference to certain preferred procedures, materials and uses, it is understood that the invention is not limited thereto, and that numerous variations may be made in the procedures herein described, and that equivalent materials may be substituted. For example, color formers and surface active agents other than those specifically mentioned and utilized in the foregoing examples may be 6 used. Accordingly, we do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. The method of incorporating in a light sensitive gelatin silver halide emulsion, a color former fast to diifusion and capable of forming upon color development with a primary aromatic amino developing agent, a dye image selected from the class consisting of azomethine, indoaniline and phenazonium dye images, said color former containing a benzimidazole nucleus connected through its carbon atoms in the 2-position to the residueof the color forming molecule which is reactive with the oxidation product of a primary developing agent and which contains a reactive group selected from the class consisting of a reactive methylene, ethenol and phenolic hydroxy group said benzimidazole nucleus being substituted on one of the nitrogen atoms by an aliphatic hydrocarbon radical containing at least 10 carbon atoms and substituted in the benzene portion by a water solubilizing group which comprises dissolving said color former in dimethyl sulfoxide, diluting the resultant solution with an aqueous solution containing a surface active agent and then adding the resultant dispersion to the liquidgelatin silver-halide emulsion prior to coating it upon a suitable. support.

2. The method of incorporating in a photographic gelatin silver halide emulsion layer, a color former stable to diffusion which is reactive with the oxidation products of a primary amino developing agent to yield upon exposure and development with a primary amino developing agent, a dye image selected from the group consisting of azomethine, indoaniline and phenazonium dyes, said color former containing a benzimidazole radical characterized by the following general formula:

wherein R is the residue of the color forming molecule and contains a group selected from the class consisting of methylene, ethanol and phenolic hydroxy groups capable of reacting with the oxidation products of the primary amino developing agent; R is an aliphatic hydrocarbon radical containing at least 10 carbon atoms; R, is a water solubilizing group and the carbon in the 2-position of said benzimidazole radical is linked to the residue of the color forming molecule which contains a reactive group selected from the group consisting of methylene, ethenol and phenolic hydroxy groups which comprises dissolving said color former in dimethyl sulfoxide, diluting the color former solution thus obtained with an aqueous solution of a surface active agent and adding the resultant solution to a liquid gelatin silver halide emulsion prior to coating the latter upon a support.

3. The method of incorporating into a gelatin silver halide emulsion layer, a benzimidazole substituted color former selected from the class corresponding to the following formulae:

C-Rr

and

wherein R is a hydroxy aromatic radical, thehydroxy I group being nuclearly attached and said radical being linked to the benzimidiazole nucleus in an ortho position. to said hydroxy group; R is an alkyl chain of at least 10,

" prises dissolving said color former in dimethyl sulfoxide,

diluting the color former solution thus obtained with a water solution of a surface active agent and adding the resultant dispersion to a liquid gelatin silver halide emulsion prior to coating the latterupon a suitable support.

4. The method of incorporating a color former into a gelatin silver halide emulsion layer as defined by claim 1,

wherein said color former is l-0ctadecyl-2[Z'-(l'-hydroxynaphthyl) ]-benzimindazole-5-sulfonic acid.

5. The method of incorporating a color formerinto a gelatin silver halide emulsionlayer. as defined by claim 1, wherein said color former is 2-.(4'-benzoylacetaminophena yl)- 1-octadecylbenzimidazole-i sulfonic acid. a 1

6. The method of incorporating a color former into a gelatin silver halide emulsion layer as defined by claim'l, wherein said color former .is '2-[(3,5'-dibenzoylacetamino)phenyl]a1-octadecylbenzimidazole-5-sulfonic acid.

7. The method of incorporating a color former into a gelatin silver halide emulsion layer as definedby claim 1, wherein said color former is 2-[4-(6-bromo 8-hydroxy-2 (2' sulfophenyl) -cinchoninoyl)-aminophenyl]-1-octadecyl-S-sulfonbenzimidazolti.

References Cited in the'fileof this patent UNITED STATES I PATENTS 2,486,440 Schmidt et al. Nov. 1, 1949 2,545,687 Craig Mar. 20, 1951 2,547,307 Craig Apr; 3, 1951 2,701,766

OTHER REFERENCES Chem; and Eng. News, Sept. 19, 1955, p. 3933.

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1. THE METHOD OF INCORPORATING IN A LIGHT SENSITIVE GELATIN SILVER HALIDE EMULSION, A COLOR FORMER FAST TO DIFFUSION AND CAPABLE OF FORMING UPON COLOR DEVELOPMENT WITH A PRIMARY AROMATIC AMINO DEVELOPING AGENT, A DYE IMAGE SELECTED FROM THE CLASS CONSISTING OF AZOMETHINE, INDOANILINE AND PHENAZONIUM DYE IMAGES, SAID COLOR FORMER CONTAINING A BENZIMIDAZOLE NUCLEUS CONNECTED THROUGH ITS CARBON ATOMS IN THE 2-POSITION TO THE RESIDUE OF THE COLOR FORMING MOLECULE WHICH IS REACTIVE WITH THE OXIDATION PRODUCT OF A PRIMARY DEVELOPING AGENT AND WHICH CONTAINS A REACTIVE GROUP SELECTED FROM THE CLASS CONSISTING OF A REACTIVE METHYLENE, ETHENOL AND PHENOLIC HYDROXY GROUP SAID BENZIMIDAZOLE NUCLEUS BEING SUBSTITUTED ON ONE OF THE NITROGEN ATOMS BY AN ALIPHATIC HYDROCARBON RADICAL CONTAINING AT LEAST 10 CARBON ATOMS AND SUBSTITUTED IN THE BENZENE PORTION BY A WATER SOLUBILIZING GROUP WHICH COMPRISES DISSOLVING SAID COLOR FORMER IN DIMETHYL SULFOXIDE, DILTUING THE RESULTANT SOLUTION WITH AN AQUEOUS SOLUTION CONTAINING A SURFACE ACTIVE AGENT AND THEN ADDING THE RESULTANT DISPERSION TO THE LIQUID GELATIN SILVER-HALIDE EMULSION PRIOR TO COATING IT UPON A SUITABLE SUPPORT. 